1. Field of the Invention
The subject invention relates to a device and method for separating heavier and lighter fractions of a fluid sample. More particularly, this invention relates to a device and method for collecting and transporting fluid samples whereby the device and fluid sample are subjected to centrifugation in order to cause separation of the heavier fraction from the lighter fraction of the fluid sample.
2. Description of Related Art
Diagnostic tests may require separation of a patient's whole blood sample into components, such as serum or plasma, (the lighter phase component), and red blood cells, (the heavier phase component). Samples of whole blood are typically collected by venipuncture through a cannula or needle attached to a syringe or an evacuated blood collection tube. After collection, separation of the blood into serum or plasma and red blood cells is accomplished by rotation of the syringe or tube in a centrifuge. In order to maintain the separation, a barrier must be positioned between the heavier and lighter phase components. This allows the separated components to be subsequently examined.
A variety of separation barriers have been used in collection devices to divide the area between the heavier and lighter phases of a fluid sample. The most widely used devices include thixotropic gel materials, such as polyester gels. However, current polyester gel serum separation tubes require special manufacturing equipment to both prepare the gel and fill the tubes. Moreover, the shelf-life of the product is limited. Over time, globules may be released from the gel mass and enter one or both of the separated phase components. These globules may clog the measuring instruments, such as the instrument probes used during the clinical examination of the sample collected in the tube. Furthermore, commercially available gel barriers may react chemically with the analytes. Accordingly, if certain drugs are present in the blood sample when it is taken, an adverse chemical reaction with the gel interface can occur.
Certain mechanical separators have also been proposed in which a mechanical barrier can be employed between the heavier and lighter phases of the fluid sample. Conventional mechanical barriers are positioned between heavier and lighter phase components utilizing differential buoyancy and elevated gravitational forces applied during centrifugation. For proper orientation with respect to plasma and serum specimens, conventional mechanical separators typically require that the mechanical separator be affixed to the underside of the tube closure in such a manner that blood fill occurs through or around the device when engaged with a blood collection set. This attachment is required to prevent the premature movement of the separator during shipment, handling and blood draw. Conventional mechanical separators are affixed to the tube closure by a mechanical interlock between the bellows component and the closure. Example devices are described in U.S. Pat. Nos. 6,803,022 and 6,479,298.
Conventional mechanical separators have some significant drawbacks. As shown in FIG. 1, conventional separators include a bellows 34 for providing a seal with the tube or syringe wall 38. Typically, at least a portion of the bellows 34 is housed within, or in contact with a closure 32. As shown in FIG. 1, as the needle 30 enters through the closure 32, the bellows 34 is depressed. This creates a void 36 in which blood may pool when the needle 30 is removed. This can result in needle clearance issues, sample pooling under the closure, device pre-launch in which the mechanical separator prematurely releases during blood collection, hemolysis, fibrin draping and/or poor sample quality. Furthermore, previous mechanical separators are costly and complicated to manufacture due to the complicated multi-part fabrication techniques.
Accordingly, a need exists for a separator device that is compatible with standard sampling equipment and reduces or eliminates the aforementioned problems of conventional separators. A need also exists for a separator device that is easily used to separate a blood sample, minimizes cross-contamination of the heavier and lighter phases of the sample during centrifugation, is independent of temperature during storage and shipping and is stable to radiation sterilization.